1. Field of the Invention
The invention relates to chromatography and, more particularly, to a method for improving the chromatographic detection limit for an analyte.
2. Description of the Related Art
In chromatography, a sample of a substance mixture to be analyzed is guided through a chromatographic separation apparatus. As a result of the different rates of movement through the separation apparatus, the analytes, i.e., the individual substances of the substance mixture, reach the outlet of the separation apparatus at different times and are detected there in succession by a suitable detector. As a measured signal, the detector produces a chromatogram, which consists of a baseline and a number of peaks corresponding to the separated substances. In practice, the chromatogram is noisy, with the individual peaks protruding more or less clearly from the signal noise. The noise corresponds to the difference between the greatest and smallest measured value in a considered section of the chromatogram without a peak, e.g., the two portions in front of and behind the peak of interest.
By way of example, the noise can also be defined as n-times the standard deviation of the measured values from their mean. The detection limit of an analyte is defined as k-times, e.g., 2-times, the noise of the baseline; i.e., the peak height measured from the noise-free baseline, i.e., from the mean of the noise, must be at least k-times the noise. In the case of well-resolved peaks, the peak area above the noise-free baseline is proportional to the concentration of the analyte, with the peak area, unlike the peak height, providing exact results even in the case of unsymmetrical peaks.
Thus, the level of the detection limit for an analyte is dependent on the accuracy with which the noise-free baseline can be established in the region of the peak of the analyte.